Reduction of GPS receiver noise using adaptive filters

The objectives of this paper are to propose and describe an adaptive interference canceling technique for estimating GPS receiver noise and to characterize the noise over a frequency band of interest. Feasibility of the technique is demonstrated using a system in which GF'S receiver noise is the major factor limiting accuracy and resolution. After a brief review of an adaptive system, it is shown how it can be applied as an adaptive interference canceler to estimate and remove GPS receiver noise using tyro receivers in differential mode. Because of its dependence on GPS-derived vehicle acceleration, an airborne gravity system provides an excellent case study to demonstrate the effectiveness and usefulness of such a noise estimation technique. To set the stage for the discussion, the concept of an airborne gravity system is briefly introduced. It is shown that for a DGPS/INS airborne gravity system, GPS measurement noise is a major error source restricting improvements in obtainable resolution and limiting accuracy at a given resolution. Preliminary results, based on actual airborne gravity measurements are then presented. These results show that the method does work and that improvements in accuracy and resolution can be achieved when compared to an independent reference. This type of noise estimation technique is by no means restricted to the example used in this paper. There are a number of other potential applications of the proposed technique in the general area of vehicle motion estimation, Some of these applications are discussed in the concluding remarks.